Exploring the Antioxidant and Structural Properties of Black Bean Protein Hydrolysate and Its Peptide Fractions

A great deal of attention has been paid to charactering the protein hydrolysates prepared by enzymatic hydrolysis, while the influence of molecular weight (MW) distributions on the resultant hydrolysates remains unclear. This study aimed to explore the physicochemical and antioxidant characteristics of protein hydrolysate and its peptide fractions. Bromelain has been commonly used to hydrolyze black bean protein via response surface methodology (RSM). The optimal hydrolysis parameters were observed at 52°C, pH 7, E/S ratio of 2.2 (ratio of enzyme to substrate), and 4 h. Under these parameters, the hydrolysate (BPH) presented DPPH radical scavenging activity and Fe²⁺ chelating activity with IC₅₀ values of 100.08 ± 2.42 and 71.49 ± 0.81 μg/mL, respectively. This might be attributed to structural characteristics, varying with different molecular weight distributions. Interestingly, among BPH and its peptide fractions, peptides smaller than 3 kDa were noted to exhibit the strongest DPPH and ABTS radical scavenging activity. More intriguingly, this peptide fraction (<3 kDa) could predominantly prolong the induction period of sunflower oil, which was, respectively increased to 1.31 folds. This may be due to high proportions of hydrophobic amino acids. Unexpectedly, the optimal Fe²⁺ chelating activity was observed in the peptide fraction measuring at 3-10 kDa, showing highly positive correlations with histidine and arginine. These identified peptide fractions derived from black bean protein can therefore be employed for food fortification acting as natural antioxidant alternatives.